The preovulatory LH surge sets in motion a chain of events that culminate in breakdown of the ovarian follicle wall and release of the egg in a process known as ovulation. Ovulation involves an inflammatory process that is characterized by a massive influx of white blood cells, known as leukocytes, to the ovary. This influx of leukocytes is critical for fertility as removal of leukocytes in experimental models blocks oocyte release. However, the factor(s) underlying the recruitment of leukocytes to the ovary are unknown. The present proposal will examine a newly identified candidate, chemokine ligand 20 (CCL20). Our preliminary data shows that mRNA for CCL20 is massively induced in the human during the early and late preovulatory stage in the granulosa and theca cells from the ovarian follicle. Yet other than our preliminary data, nothing is known as to temporal patterns of expression, the regulation, or function of CCL20 and its receptor CCR6 in the ovary. The present proposal builds on these provocative findings and will test the overall hypothesis that the LH surge stimulates an increase in CCL20 and the increase in this chemokine results in recruitment of leukocytes that impact events necessary for ovulation. This hypothesis will be addressed using a unique model where the granulosa and theca from human periovulatory follicles will be collected prior to and at three designated times after hCG to induce ovulation (early, late and postovulatory). These human samples will be compared and contrasted to changes in CCL20 and CCR6 in the rat ovary using a well characterized rodent model for ovulation. This will be accomplished by the following three Aims. Aim 1 will determine the changes in the expression of the CCL20 and CCR6 system in both the human and rat ovary. This Aim will also determine how CCL20 and CCR6 expression is regulated via the major ovulatory pathways induced by LH. Aim 2 will explore the role of CCL20 in leukocyte recruitment into the ovary using well-characterized migration and invasion models. Due to the potential role of CCL20 to regulate cellular differentiation, Aim 3 will investigate the role of CCL20 on ovarian cell function, specifically the ability of granulosa cells to survive, differentiate, and make sterid hormones. Additionally, the impact of CCL20 on ovarian cells will be assessed using microarray technology. The major strengths of the current proposal lie in the use of well characterized human preovulatory follicles as a foundation to understand the cellular expression, regulation, and the impact of CCL20 on the events associated with ovulation in the human and, our integrated comparative approach across species to elucidate the role that this chemokine plays in the ovulatory process. Nothing is known about CCL20 and its receptor in the ovary. As such, the proposed studies are extremely timely to elucidate the role that this chemokine system plays in the coordinated processes of follicular rupture and oocyte release which are fundamental aspects of normal human ovarian physiology.